Growth and Viability of Cryptococcus hominis at Mouse and Rabbit Body Temperatures

Abstract

Mice were readily infected with strains of Cryptococcus hominis isolated from human cases of torula meningitis, subcutaneous tumor, and generalized infection. 1 Death occurred following a regular increase in the number of viable yeasts in the mouse tissues, especially in the brain and lungs. On the other hand, rabbits resisted infection and the number of viable yeasts in the tissues decreased regularly, even when very large doses of cryptococci were given intravenously. Mice and rabbits each were found to produce only a very low grade acute cellular reaction when the yeasts were injected intraperitoneally. 2

When the normal body temperatures∗ of mice were compared with those of rabbits and especially when it was noted that mice failed to produce fever with experimental cryptococcus infection, whereas the temperatures of injected rabbits readily rose to 105°–107°F (40.6–41.7°C), the writer decided to determine if the growth and viability of C. hominis at rabbit and mouse body temperatures was significantly different.

Six strains of group III cryptococci (Benham grouping 3 ) which were isolated from human cryptococcus infections during the past 5 years were inoculated into dextrose veal infusion broth (pH 7.0) and grown at 99°F (37.3°C), 101°F (38.3°C), 103°F (39.4°C), 105°F (40.6°C), and 107°F (41.7°C). At the higher temperatures fewer organisms were produced and viable cells (determined by plating in Sabouraud's dextrose agar) decreased, in number. The effect on the number of viable cells of one of the strains of C. hominis is shown in Table I.

At 105°F (40.6°C) viable cells had decreased in number after 3 hours' incubation, at 107°F (41.7°C) they decreased within an hour and only 2.5% survived at the end of 24 hours.

The total number of yeast cells was also counted (hemacytometer) in tubes of dextrose veal infusion broth and Sabouraud's dextrose broth incubated at 22°, 29° and 36°C.